Is it normal to be friends with a past lover?

FarnboroughBoy11:
First of all this is not a wind up and I’m a bit embarrassed asking on here but my mind just wonders all day when I’m driving so want to get other peoples opinions.

Basically I’ve started seeing this bird, she has been a good mate for about 4 years but there’s always been something else there between us. We have properly been seeing each other for about 4 months now and it’s going good except something that I can’t get my head around.
She is good mates with a fella that she slept with a few times when she was about 18/19… She’s 25 next month.
I completely beleive her when she says she doesn’t feel a single thing for him and in fact she gets pretty ■■■■■■ off whenever I insinuate something on the subject.
She is in a group of friends that are very close, mixed between boys and girls and they often go out together and have BBQs etc

Like I say she is a good girl and we like each other alot. I just can’t help feeling that I might be being a bit of a mug, my mind wonders all over the place at work and sometimes I just feel like letting her go because it’s eating away at me.
What do you think?

Let her go,it will just eat away at you,there’s plenty of fish out there,and the right one is amongst them.you know when you meet that one